Well, while I was browsing through the children of morrowind esm, I realized something. You know that invisible twit that gets you to help him? COM doesn't turn him into a teenager! So, filled with the blood wrath of a thousand dying suns, I fired up the CS and fixed this atrocity! More seriously, All this does is add a new race (im_teen) that's a tiny bit taller than the COM "kids" race, and changes Cassius Olcinius to that race. From the readme:

This is just a small plugin to change Cassius Olcinius (the invisible son) into a teenager, instead of being an adult.It requires Children of Morrowind v2. Make sure it is set to load after anything that edits this npc. No special instructions, just plug n' play.